1. Field of Endeavor
The present invention relates to membranes and more particularly to preparation of membranes using solvent-less vapor deposition followed by in-situ polymerization.
2. State of Technology
U.S. Pat. No. 5,817,165 for fluorine-containing polyimide gas separation membrane and method of manufacturing the same issued Oct. 6, 1998 to Hisao Hachisuka et al provides the following state of technology information: “Polyimide is known as a gas separation membrane material with excellent heat-resisting and anti-chemical properties due to its high glass transition point and rigid molecular chain structure. The manufacture of a thinner and more asymmetric separation membrane having a mechanical strength suitable for practical usage has been considered. When a polymer having a high separation factor is formed as a membrane on a proper porous supporting film, the membrane preferably should be 0.1 μm thick or less to obtain a practical permeability. As a result, the manufacturing process becomes complicated, the yield deteriorates and the cost is raised, and thus it is impractical for industrial use.”
U.S. Pat. No. 6,497,747 for production and use of improved polyimide separation membranes issued Dec. 23, 2002 to Yong Ding et al provides the following state of technology information: “The use of polymeric membranes for gas separation applications is well documented in the art. The relationship between the polymeric structure and the gas separation properties has been extensively studied, see for example, W. J. Koros, Journal of Membrane Science, Volume 83, pp 1, 1993; L. M. Robeson, Journal of Membrane Science, Volume 62, pp 165, 1991; and L. M. Robeson, Polymer, Volume 35, pp 4970, 1994. It is well documented in the art that stiffening the polymeric backbone while simultaneously inhibiting chain packing can lead to improved gas permeability combined with an increase in gas selectivity for certain gas mixtures. Polyimides are examples of such rigid-rod polymers showing desirable gas separation properties, see for example, D. R. B. Walker and W. J. Koros, Journal of Membrane Science, Volume 55, page 99, 1991; S. A. Stern, Journal of Membrane Science, Volume 94, page 1, 1994; K. Matsumoto, P. Xu, Journal of Applied Polymer Science, Volume 47, page 1961, 1993. U.S. Pat. Nos. 4,705,540; 4,717,393; 4,717,394; 5,042,993; and 5,074,891 disclose the preparation of such aromatic polyimide gas separation membranes. For practical industrial applications polymeric gas separation membranes are fabricated into an asymmetric or a composite configuration with thin separation layers. The membranes can be further configured into flat sheets or into hollow fibers. Although rigid-rod polyimides have excellent gas separation properties, they frequently can be dissolved only in aggressive organic solvents such as N-methyl-pyrrolidinone (NMP), N,N-dimethyl formamide (DMF), or phenols which makes it difficult to prepare composite membranes with ultrathin separation layers and can further cause environmental problems. For example, polyimide membranes have been fabricated from chlorophenol solutions as described in U.S. Pat. No. 4,440,643.”